This invention relates generally to synthetic jet actuators and more particularly to synthetic jet actuators operated by piezoelectric actuators.
It is known to use a synthetic jet to influence the flow over a surface, for example to control flow separation from an airfoil. A typical synthetic jet actuator comprises a housing defining an internal chamber. An orifice is present in a wall of the housing. The actuator further includes a mechanism in or about the housing for periodically changing the volume within the internal chamber so that a series of fluid vortices are generated and projected in an external environment out from the orifice of the housing. Various volume changing mechanisms are known, for example a piston positioned in the jet housing to move so that fluid is moved in and out of the orifice during reciprocation of the piston, or a flexible diaphragm as a wall of the housing. The flexible diaphragm is typically actuated by a piezoelectric actuator or other appropriate means.
Typically, a control system is utilized to create time-harmonic motion of the diaphragm. As the diaphragm moves into the chamber, decreasing the chamber volume, fluid is ejected from the chamber through the orifice. As the fluid passes through the orifice, the flow separates at the sharp edges of the orifice and creates vortex sheets which roll up into vortices. These vortices move away from the edges of the orifice under their own self-induced velocity. As the diaphragm moves outward with respect to the chamber, increasing the chamber volume, ambient fluid is drawn from large distances from the orifice into the chamber. Since the vortices are already removed from the edges of the orifice, they are not affected by the ambient fluid being entrained into the chamber. As the vortices travel away from the orifice, they synthesize a jet of fluid, a xe2x80x9csynthetic jet,xe2x80x9d through entrainment of the ambient fluid.
However, the prior art devices have relatively limited capacity, in that they use only a single moving element or a moving element of limited deflection. It would be desirable to obtain increased performance of synthetic jet actuators.
Accordingly, there is a need for a synthetic jet actuator having greater capacity than previous devices.
The above-mentioned need is met by the present invention, a first embodiment of which provides a synthetic jet actuator in the form of a flexible piezoelectric actuator blade disposed in a wall of a flowpath, such as an airfoil. In another embodiment, a synthetic jet actuator is provided in which a pair of bimorph piezoelectric plates are connected by a flexible hinge.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.